1. Field of the Invention
The present invention relates to a liquid jet head for ejecting a liquid from a nozzle to form images, characters, or a thin film material onto a recording medium. The present invention relates also to a liquid jet apparatus using the liquid jet head, and to a method of manufacturing a liquid jet head.
2. Description of the Related Art
In recent years, there has been used an ink-jet type liquid jet head for ejecting ink droplets on recording paper or the like to render characters or graphics thereon, or for ejecting a liquid material on a surface of an element substrate to form a functional thin film thereon. In such a liquid jet head, ink or a liquid material is supplied from a liquid tank via a supply tube to the liquid jet head, and ink or a liquid material filled into a channel is ejected from a nozzle which communicates with the channel. When ink is ejected, the liquid jet head or a recording medium on which a pattern of jetted liquid is to be recorded is moved to render a character or a graphics, or to form a functional thin film in a predetermined shape.
Japanese Patent Application Laid-open No. 2009-196122 describes an ink jet head 60 in which ink channels which are a large number of grooves are formed in a sheet formed of a piezoelectric material. FIG. 14 is a sectional view of the ink jet head 60 illustrated in FIG. 2 of Japanese Patent Application Laid-open No. 2009-196122. The ink jet head 60 has a laminated structure of a substrate 62, a piezoelectric member 65, and a cover member 64. Supply ports 81 are formed in the middle of the substrate 62 and discharge ports 82 are formed so as to sandwich the supply ports 81. The piezoelectric member 65 and a frame member 63 are adhered to a front surface of the substrate 62, and the cover member 64 is adhered to an upper surface thereof.
The piezoelectric member 65 is formed by adhering together two piezoelectric plates 73 in which the directions of polarization are opposite to each other. A plurality of minute grooves which extend in a sub-scanning direction (in a direction in parallel with the drawing sheet) are formed by cutting in the piezoelectric member 65, and a plurality of pressure chambers 74 which are arranged at regular intervals in a main scanning direction (in a direction perpendicular to the drawing sheet) are formed. Each of the pressure chambers 74 (channels) is defined by a pair of adjacent walls 75. An electrode 76 is formed continuously on opposing side surfaces of the pair of walls 75 and a bottom portion therebetween, and further, is electrically connected to ICs 66 via electric wiring 77 formed on the front surface of the substrate 62. The cover member 64 is formed by adhering a film 92 and a reinforcing member 94 together via an adhesive. The cover member 64 is adhered to the piezoelectric member 65 and the frame member 63 under a state in which the reinforcing member 94 is on the piezoelectric member 65 side. Openings 96 and nozzles 72 which correspond to the pressure chambers 74 are formed in the reinforcing member 94 and in the film 92, respectively.
Ink is supplied from the supply ports 81 in the middle of the substrate 62, and flows to the plurality of pressure chambers 74 and then to an ink chamber 90 to be discharged from the discharge ports 82. When a drive pulse is applied from the ICs 66 via the electric wiring 77 to the electrode 76 on the pair of walls 75 sandwiching the pressure chamber 74, the pair of walls 75 undergo shear mode deformation and bend so as to be spaced away from each other, and then return to their initial positions to increase the pressure in the pressure chamber 74, which is accompanied by ejection of an ink droplet from the corresponding nozzle 72.
Here, as the film 92 of the cover member 64, a polyimide film is used, and, as the reinforcing member 94, a metal foil of, for example, SUS, Ni, Ti, or Cr is used. If the cover member 64 is the single layer polyimide film 92, the nozzles 72 may be formed easily in such a polyimide film by a laser, but the stiffness of such a polyimide film is lower than that of a metal or the like, and thus, when the walls 75 undergo shear mode deformation, the film is extended. Therefore, pressure cannot be transferred efficiently to ink filled into the pressure chambers 74. Accordingly, as the cover member 64, the polyimide film 92 and the metal foil having a stiffness higher than that of the polyimide film 92 are adhered together. This enables fixing of upper ends of the walls 75 when the walls 75 undergo shear mode deformation, and pressure loss when an ink droplet is ejected may be eliminated. Note that, the polyimide film 92 has a thickness of 50 μm and the metal foil as the reinforcing member 94 has a thickness of 50 μm to 100 μm. Further, in order to prevent a short circuit between the electrode 76 formed on wall surfaces of the walls 75 and the metal foil as the reinforcing member 94, an SiO2 film 95 is formed on a surface of the metal foil on the electrode 76 side.
However, an ejection surface of an ink jet head ordinarily has a length of several tens of millimeters or more. A metal foil having a thickness of 50 μm to 100 μm and having an outside diameter of several tens of millimeters or more is liable to suffer warping and is difficult to adhere in a flat state to upper end surfaces of the walls 75 via an adhesive. Further, it is also difficult to prevent warping when the polyimide film 92 having a thickness of 50 μm and this metal foil are adhered together via an adhesive.
Accordingly, a method is conceived in which a thick metal plate is first adhered to the upper end surfaces of the walls 75 and then the metal plate is ground to the above-mentioned thickness to be a metal foil. In this case, the openings 96 are in advance formed in the metal plate, and the metal plate is ground to be a thin film. However, if the metal plate is ground, ends of the openings 96 are deformed or a burr is formed thereat and the shape of the openings 96 may not be maintained. Further, if the reinforcing member 94 is formed of a metal material, such a metal material causes a short circuit with the electrodes 76 formed on the wall surfaces of the walls 75. In order to prevent this, it is necessary to form the SiO2 film 95 on the surface of the metal material, which increases the number of steps to increase the cost. Further, the metal foil as the reinforcing member 94 is in contact with ink. Therefore, if corrosive ink is used, the metal material may be corroded to reduce the durability of the ink jet head.